One type of power supply topology is a flyback topology. Typically, a power supply that uses a flyback topology includes a flyback transformer and a switching device. When the switching device is turned on, a voltage is applied to the primary winding of the flyback transformer. When the switching device is turned off, the secondary winding of the flyback transformer conducts energy through a rectifier diode into an output capacitor where the energy is stored.
Power supplies often incorporate a current limiting function that is used to limit the amount of current output by such power supplies. Typically, a current sensing device is used to determine the amount of current output by a power supply at a given point in time. The operation of the power supply can then be adjusted based on the sensed output current, if appropriate.
Power supplies that use a flyback topology typically include a current sensing resistor in series with the secondary winding of the flyback transformer to sense the amount of current output by the power supply. Because this current sensing resistor is in series with the secondary winding of the flyback transformer, the current sensing resistor carries a high amount of current and dissipates a large amount of heat. As a result, the current sensing resistor is typically physically large and relatively costly.